Although it is only fairly recently that the importance of trace elements in plant nutrition has been established, enormous advances have been made in this field of research and numerous publications of considerable scientific and economic importance, dealing with the subject, have appeared. The physiological functions of zinc in promoting plant growth have not all been satisfactorily identified as yet. There are indications, however, that zinc acts as a catalyst or regulator in plant metabolism. It appears too, that the element plays some role in chlorophyll formation. Zinc deficiency is associated with leaf chlorosis and a general collapse of v ital processes. The analysis of leaves and soils has become an essential part of the study of the nutritional diseases of plants and it is imperative that accurate and reliable methods of analysis should be available. Intro. p. 1.

1. Accurate and reproducible methods for the determination of N and acid- extractable P in soils are described. The variations in N, P, and K found by intensive sampling of three different soil types are presented. 3. Suggestions for the adequate sampling of soils for various purposes arc given. 4. A study is presented of the preparative stages in leaf analysis (washing, drying, grinding and storage) as applied to citrus and pineapple leaf material. Likely errors are pointed out and procedures whereby these may be minimised are described. 5. A reliable wet-ashing procedure for obtaining leaf solutions is described. 6. Accurate and reproducible methods for the determination of total N, P,. K, Ca, Mg, Na, Fe, Mn, Zn and Cu in citrus and pineapple leaves are presented. 7. It is shown that diurnal variations in nutrient concentrations occur in citrus and pineapple leaves. 8. The variations in N, P, K, Ca, Mg, Na, Fe, Mn, Zn and Cu, occurring from tree to tree in 3 different Navel orange blocks are presented. It is shown that if all these elements are to be represented . to within 10% of the mean values on a 19 : 1 probability level, all the trees in the blocks would have to be sampled. Reasonable sampling procedures for various purposes are suggested. 9. The variations in N, P, K, Ca, Mg, Fe, Mn, Zn and Cu, occurring in 3 different Cayenne pineapple plantations are presented and described. Suitable sampling procedures are suggested.

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No description available.

Master of Science

Artificial and natural weathering studies were conducted on four dioctahedral micas found in soil parent material of the Virginia Piedmont. Emphasis was given to the relationship between loss of K (also Na in certain cases), increase in CEC, and expansion characteristics. Boiling treatments with several different solutions were used to promote artificial weathering. In terms of the three parameters of primary interest, the results were of three general types, depending upon the nature of the boiling medium. Boiling solutions of HCl and HOAc removed K and Na, but produced only slight expansion and a negligible increase in CEC. The acid solutions, being at low pH, liberated from the mineral large amounts of Al, which likely underwent hydrolysis later to form hydroxy-Al polymeric groups. These groups can occupy exchange sites, but they remain nonexchangeable. Boiling aalt solutions of NaCl and MgCl₂ removed K and Na in large amounts, produced considerable, but only a slight increase in CEC resulted. The explanation for the small increase in CEC was believed to be due also to blocking of exchange sites by nonexchangeable hydroxy-Al groups, because salts tend to accelerate the hydrolysis reaction. A boiling Na-citrate solution removed K effectively, produced marked expansion, and caused a large increase in CEC. Citrate complexes Al, which probably accounted for the high CEC. When a sample was treated with hot HCl prior to Na-citrate boiling, the loss of K and increase in CEC was stoichiometric. The equivalence was attributed to the removal of amorphous material by HCl and complexing of Al by Na-citrate. Vermiculite and kaolinite were the natural weathering products of the dioctahedral micas studies. There was a striking similarity between the artificially-produced vermiculite and that occurring under natural conditions. The product formed under both circumstances expanded to approximate 14 A. when glycerol-solvated and contracted to 10 A. upon K-saturation and heating. Although the artificial weathering media were not representative of natural weathering conditions, the basic mechanism of mica alteration apparently was similar. The soil micas altered easily in the laboratory compared to an Ontario muscovite. Thus, it was concluded that soil micas are quite different from the specimen-type micas. They may possess a lower charge or lack the structural control of specimen muscovites. The difference in ease of weathers between dioctahedral and trioctahedral micas likely is attributable to the difference in chemical composition, especially in the octahedral layer. Dioctahedral micas appear to be more strongly bonded than trioctahedral micas as a result of the higher-charged Al⁺⁺⁺ ion in the octahedral layer. This stronger bonding would tend to restrict initial alteration. Subsequent alteration also would be hindered because, as weathering proceeds, greater hydrolysis of Al in dioctahedral micas would result in more fixation of positively-charged hydroxy-Al polymers in the interlayer position. This fixed Al inhibits expansion of dioctahedral micas. In trioctahedral micas, which contain Fe and/or Mg, this type of fixation does not occur during acidic weathering. A significant finding was the occurrence of paragonite, the Na analogue of muscovite, in intimate association with muscovite. A relatively constant Na/K molar ratio of approximately one was maintained in both the parent rocks and soils. This indicated that equal molar quantities of paragonite and muscovite were present and that weathering of the two micas was similar. Paragonite is believed to be more widespread occurrence than previous work has indicated. Its influence on soil genesis, morphology, and classification may be significant. / Ph. D.

Please read the abstract in the section 00front of this document / Dissertation (MSC (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted

LD2668 .T4 1941 B82 / Master of Science

Call number: LD2668 .T4 1979 H47 / Master of Science

No description available.